Document any situations where the TC JDBC driver needs to be explicitly configured

[rnorth]

#304 covered a case where this needs to be done for Spring Boot.
Are there any other cases where the developer has to manually select the TC JDBC driver for driver-based testing?

[bsideup]

@rnorth shall we close it after 1 year of inactivity? :D

[kiview]

I think we will find other examples once a problem occurs in real life usage, so it should be okay to close this^^